1. Field of the Invention
This invention relates generally to the field of telephonic switching systems and methods and, more particularly, to such telephonic switching systems and methods having a multiport switch with a distributed architecture in which signaling information is conveyed to the multiport switch of the telephonic switching system over multichannel links.
2. Description of the related art including information disclosed under 37 C.F.R. .sctn.1.97-1.99
Digital telephonic switching systems employing a multiport switch having a central control circuit for distributing information received over a multichannel link from another sending switch are well known. It is also known in such telephonic switching systems to have a distributed architecture in which the processing of information is performed at a variety of peripheral circuits, and the resultant data is sent to the central control circuit for further processing with the data received from other multiport switches. A distributed architecture is advantageous in digital telephonic switching systems since distributed processing is often an efficient means of enhancing computer processing power by having each peripheral circuit preferably devoted to a specialized task. Examples of such telephonic switching systems are shown in U.S. patent application Ser. No. 07/770,197 of Jones et al. entitled "Multichannel Telephonic Switching Network With Different Signaling Formats and Connect/PBX Treatment Selectable For Each Channel", filed Oct. 2, 1991, now U.S. Pat. No. 5,268,903 ; U.S. Pat. No. 5,140,611 of Jones et al. entitled "Pulse Modulated Self-Clocking and Self-Synchronizing Data Transmission and Method for a Telephonic Communication Switching System", issued Aug. 18, 1992; U.S. Pat. No. 5,127,004 of Lenihan et al. entitled "Tone and Announcement Message Code Generator for a Telephonic Switching System and Method", issued Jun. 30, 1992 and U.S. Pat. No. 4,627,047 of Pitroda et al. entitled "Integrated Voice and Data Telecommunications Switching System", issued Dec. 2, 1986.
Typically in such digital telephonic switching systems or telecommunication systems, signaling information is conveyed from a sending multiport switch to a receiving multiport switch over multichannel circuits for the purpose of making individual voice connections. The forms of the signalling information sent over the multichannel link involves the sending switch sending certain signaling bits on the multichannel link to convey to the receiving switch that a channel is being seized. The channel is seized on the receiving switch preferably for the purpose of making a connection between the switches in order for certain data such as dual tone multiple frequency (DTMF) tones to be sent over a pulse code modulation (PCM) path at 64 Kbits per second. The data in the form of DTMF tones is sent on the seized channel to identify to the receiving switch the specific party being called at the sending switch.
In such known telecommunication systems there are several types of trunks in which the interval period is quite short between the time an indication of channel seizure is made and the time at which a stream of DTMF tones are initially sent to the sending switch. Frequently, these short interval time periods between channel seizure and data sending between two switches is seen in a variety of European switching systems employing an E-1 digital telephony format. Disadvantageously, for a multiport receiving switch having a distributed architecture, interface with a sending switch having trunks with a short interval between channel seizure and the start of data transmission is frequently very problematic. The data transmitted between a sending switch and a receiving switch is often sent in the form of DTMF tones. Switches having a distributed architecture have various peripheral circuit elements performing different functions such as: signaling bit interpretation, DTMF tone detection and interpretation, assignment of channel connections and overall switch control. However, with the distribution of functions to a plurality of peripheral circuits, a significant amount of time is spent coordinating the activities of each peripheral circuit element and ultimately performing the appropriate action within the system. Unfortunately, the time interval needed to control and coordinate all the activities between the peripheral circuits and the central control circuit often is longer than the time period between the channel seizure and the receipt of incoming information.
In a situation where DTMF tones are sent from a sending switch to a receiving switch, an adequate amount of time frequently is not available to assign a DTMF receiver at the receiving switch in order to appropriately interpret the incoming DTMF tones. Disadvantageously, since the time interval between a seizure of a channel and the sending of information is shorter than the time interval needed to prepare and coordinate the peripheral circuits in a distributed architectured switch, some or all of the incoming information will be missed by the receiving switch. Thus, the receiving switch cannot interpret an incoming DTMF tone stream and the switch is unable to properly service a telephonic call.